In applications where accurate movements are required, stepping motors, the rotation angle of which is controllable, are conventionally used instead of DC motors, and in image sensing apparatuses such as digital cameras and digital video cameras, stepping motors are used to achieve, for example, zooming. As a control device for controlling a stepping motor, a type that controls a stepping motor by constant-current chopper driving is disclosed (see, for example, Patent Publication 1).
For the purpose of keeping the motor drive current constant, a drive circuit incorporated in such a stepping motor using a constant-current drive system compares, by using a comparator, a voltage across a current-detection resistor for detecting a current flowing through the motor with a reference voltage set by a reference voltage division resistor, and, according to the comparison result, turns on or off the current that flows into the motor.
However, the above described drive circuit of the stepping motor controlled by a constant-current drive system typically needs to be provided with a number of analog circuit components such as a comparator, and thus, inconveniently, distortion of a sinusoidal wave is caused by offset adjustment, variations among individual devices, or the like. Particularly, around a midpoint, zero-cross distortion occurs, causing noise. Such being the case, when a constant-current drive system is used in a zoom-motor drive circuit of a digital video camera, the microphone of the digital video camera inconveniently picks up the noise.
Furthermore, a constant-current drive system needs to be provided with a current-detection resistor, and the current-detection resistor inconveniently consumes extra electric power.
Another controlling method for controlling a stepping motor, in which a stepping motor is controlled by a constant-voltage drive system instead of a constant-current drive system, is disclosed. In a constant-voltage drive system, a constant voltage is applied to a motor and coils are so switched as to be energized in rotation. Thus, there is no need for circuit components such as a comparator and the like which are necessary in a constant-current drive system for the purpose of keeping the current value constant. Thus, a constant-current drive system produces no distortion of a sinusoidal wave. In addition, there is no need for a resistor for current detection, either. Therefore, as compared with a constant-current drive system, a constant-voltage drive system is advantageous also from the viewpoint of power consumption.
Patent Publication 1: JP-A-2002-78385